Landau theory of free standing and epitaxial ferroelectric film
| dc.contributor.author | Musleh, Ahmad M. A. | |
| dc.date.accessioned | 2014-11-03T02:07:01Z | |
| dc.date.available | 2014-11-03T02:07:01Z | |
| dc.date.issued | 2009 | |
| dc.description | PhD | en_US |
| dc.description.abstract | Landau-Ginzburg-Devonshire’s (LGD) theory and Landau Khalatnikov’s dynamic equation are used to study the polarization reversal of second order ferroelectric (FE) systems. These FE systems that we considered are FE films with finite value of surface polarization and also films where the surface polarization can be considered as zero value. This zero surface polarisation could be the result of non-ferroelectric sites present at film surfaces. Another FE system considered is a one dimensional finite size system which is made up of (2N+1) sites with the edges at the –Nth and +Nth sites. When an external electric field is applied, all the sites including the edges feel the same field. Various forms of electric fields such as step field, sinusoidal field, triangular field and bipolar field are used to study the switching phenomena in these FE systems. The influence of the amplitude and frequency 0 E ω of the applied electric field, temperature T, film thickness L and surface parameter δ on polarization reversal have been investigated. Runge-Kutta (R-K) method and finite difference technique are the numerical techniques used to obtain the equilibrium initial polarization profile for the film of finite surface polarization and for the system of finite-size. A trial cosine function is used to obtain the initial polarization profile of FE film with zero surface polarization. The controversial thickness dependence of coercive field in FE film reported in experimental studies, can be explained theoretically by the signs of δ , the extrapolation length. For negative δ , increases with decreasing film thickness, while for positive δ , decreases with decreasing film thickness. The coercive field of FE film is found to be thickness dependent. It is interesting to note that the numerical values of switching time and the applied field are best fitted by an exponential function with high regression factor. From this curve, it has clearly shown that the FE film will only be switched by a minimum electric field . Regarding the FE film with zero surface polarization, two peaks in the switching current are found for a relatively thick film. The extra peak in the switching current is due to the dipole moments near the surface are switched earlier than the dipole moments in the interior. The effects of misfit strain on the phase transition, spontaneous polarization, transition temperatures and critical thickness of epitaxial Barium Titanate BaTiO3 are examined by using LGD free energy with the order parameter up to the eight-order because of the high compressive stress caused by the substrate interface. Phase transition of epitaxial BaTiO3 film is found to be of second-order, though the stress free BaTiO3 film undergoes first-order phase transition. The misfit strain in BaTiO3 films increases the average polarization and the transition temperature in films are shown for thicknesses up to the 1.2 nm. From our calculations, we predicted that the critical thickness of strained BaTiO3 film is 0.8 nm. | en_US |
| dc.identifier.uri | http://hdl.handle.net/123456789/183 | |
| dc.language.iso | en | en_US |
| dc.subject | Science Physic | en_US |
| dc.subject | Landau theory | en_US |
| dc.subject | Ferroelectric film | en_US |
| dc.title | Landau theory of free standing and epitaxial ferroelectric film | en_US |
| dc.type | Thesis | en_US |
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